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Possessed Wipers

582 views 6 replies 5 participants last post by  281lxm 
#1 ·
One of the many beloved idiosyncrasies of my 300SD is that the wipers occasionally activate for strange reasons. Anything from starting the car, to turning on the lights, to the AC compressor engaging can sometimes cause them to spontaneously cycle once or twice. Given the infrequency, this rather benign behavior was low on my list of priorities... until today.

It's now happening in response to almost any change in electrical system draw, and they sometimes keep running for a minute or longer with no way to stop them. We had our first real cold snap today (mid twenties all day), and I do wonder if that exacerbated the problem?

The intermittent wiper relay is at the top of my list, but since I don't have a spare handy, I thought I'd consult the experts before spending any money. The wipers do work just fine on all speeds when controlled by the wiper switch. A search of this and other forums didn't turn up anything similar I'm afraid. I've included a picture of the wipers not running for reasons unknown to me.
 

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#3 ·
For posterity's sake, this was solved by replacing the wiper relay. Near as I can tell upon disassembly, the relay spring had failed and the contact was floating. Any induction of a magnetic field nearby (e.g., from other relays) would cause it to flutter and activate the wipers. Another curious electrical mystery solved.

Next up: my recently intermittent tachometer...
 
#5 ·
maybe your old relay needed a vacation to relieve the tension :D
It looked like an original part, so after 33 years, it probably earned that vacation. I'm not sure the all expenses paid, one-way ticket I arranged to the local landfill qualifies though.
 
#7 ·
Lurp, if you get a chance with the Gen1 sedan, disconnect the negative cable on the battery and wrap a towel around it (you are not dumb but folks will read this and ask). Pull your cluster out and connect a ground wire from the metal screw on the tach side, to the gang of grounds on the chassis. Be sure to use a long enough wire to be able to freely remove your cluster without gymnastic or yoga moves. I helped a friend and we put a 6" lead wire with a female end, then a longer wire from the chassis ground point to with a male end (shrouded in vinyl). Anyway, sometimes that helps the issues as well on the Tach and Clock.
 
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